1. Field of the Invention
This invention relates to editing techniques and, more particularly, to video editing of a common scene that was recorded asynchronously by, for example, different cameras on respective source media. The present invention also relates to an editing technique wherein time delays that may be imparted to a reproduced video signal that is processed for special effects are compensated such that the processed video signal is recorded at a proper location on an edited record medium. The invention further relates to an improved technique by which edit points in one of several prerecorded scenes may be modified without requiring any modification of the edit points in the remaining scenes.
2. Description of the Prior Art
Video editing systems are well known for merging segments of video program information from different prerecorded source media, such as from different video tapes, onto a final record tape, sometimes referred to as the edit tape. Typically, an operator, or editor, monitors the video programs reproduced from each video tape, selects so-called cut-in and cut-out points from each tape and then re-records each segment defined by its cut-in and cut-out points onto the edit tape. Conventionally, video tapes have recorded thereon address data in the form of time codes to identify discrete positions, or video frames recorded on the tape. In one broadcast standard, such as the SMPTE standard, such time code address data is in the form of hours, minutes, seconds and frames, all referenced to or derived from a time code generator (or other clock, such as a studio clock). Thus, segments on each video tape may be identified by the time codes associated with the beginning (or cut-in point) and ending (or cut-out point) of those segments.
Once the editor establishes the cut-in and cut-out points (also referred to herein as the edit points) on each tape, editing is effected by playing back those source tapes by respective VTR's; and when the first cut-in point is reached, the segment of video program information identified thereby is played back and recorded on the edit tape until the cut-out point of that segment is reached. Usually, the cut-in point of the next segment on another video tape is reached in synchronism with the cut-out point of the segment just played, thus initiating the recording of this next segment on the edit tape. The foregoing operation is repeated from cut-in point to cut-out point and from tape to tape such that, as a result, the selected segments of video information are recorded sequentially on the edit tape.
While the foregoing editing operation may be carried out efficiently and quickly for relatively simple video programs, certain difficulties arise when artistic effects are desired. For example, in recording one of several scenes in sequence, a number of video cameras may be used to record the same scene concurrently from different angles on different video tapes. For instance, if three separate cameras (and, of course, three separate video recorders) are used to record video and audio signals picked up from a particular scene, each video tape will have video and audio information representing that scene recorded thereon. Since each camera is independently manually operated, when a director decides to terminate the recording of that scene, it is likely that each cameraman will end his recording at a different location. Hence, although a common scene is recorded from different angles, the length of the video program recorded on each tape will differ. As a numerical example, and assuming that each video tape begins at the same reference location (such as a time code of 00:00:00), the end of that scene on the first tape may occur at time code location 05:00:00, whereas that scene may continue to be recorded on the next tape until the time code location 05:03:00 and the end of that scene may be recorded on the third tape at the location 05:06:15. Then, when the next scene is recorded by these cameras, the beginning of that next scene may commence from the locations at which the previous scene ended; but here too, the end points of that next recorded scene may differ from tape to tape. Furthermore, each cameraman may begin his recording from a different time point in that scene such that some information recorded on one tape may not be recorded on another. For example, one cameraman may delay by a second or two the beginning of the recording operation, thus missing the information in the first one or two seconds of that scene.
As the foregoing operation continues, differences in the time codes at which a particular scene begins will accumulate from tape to tape. For example, after several scenes have been recorded, a particular scene may commence at time code location 50:30:00 on one tape, but at 63:15:00 on another and at 46:40:00 on yet another. When segments of that scene are to be edited, the editing operation is not as simple and straightforward as mentioned above. For example, assuming that both audio and video signals are recorded on the respective tapes, if the same scene is recorded by different cameras, it is important that, when a segment from one tape is added to a segment from another, both the video and the audio signals from the two tapes be in phase (or synchronized) with each other. If such phase synchronism is not maintained, noticeable discontinuities, particularly in the audio signals, will be detected. This not only is disturbing, it is unacceptable in edited programs of better quality. Thus, when editing video program information that is recorded on separate tapes but represents a common scene, all tapes must be aligned at a common location in the scene before segments thereof can be merged onto the edit tape. Heretofore, such alignment has relied primarily on the skill of the editor to position the tapes at the common scene location when the editing operation is to begin.
Another difficulty in editing arises when special effects are to be imparted to the video signals reproduced from one or more of the video tapes. In a basic editing operation, the cut-in and cut-out points on a source tape as well as those on the edit tape are selected. It is expected that the cut-in points of the source and edit tapes are reached concurrently, whereupon the video program information played back from the source tape is recorded on the edit tape. This operation assumes that there are substantially no noticeable time delays between the playing back of the video program information from the source tape and the recording of that information on the edit tape.
However, when image processing is used to produce special effects, a time delay may be imparted to the reproduced video signals by the image processing apparatus. Consequently, since the source and edit tapes are driven in synchronism to and through their cut-in points, a blank portion will remain on the edit tape following its cut-in point until the delayed, processed video signal finally reaches the edit tape for recording. This blank interval corresponds to the time delay attributed to the image processing apparatus and, depending upon the special effects which are desired, may be variable and unpredictable.
To prevent the aforementioned undesired blank interval from being recorded during an edit operation, a highly skilled editor may delay the movement of the edit tape to compensate for the time delay added to the processed video signal. However, if segments of video program information from different tapes are merged onto the edit tape, synchronous in-phase movement of all tapes is needed, thus preventing the editor from delaying movement of the edit tape. Consequently, the undesired blank interval cannot be avoided easily.
Yet another drawback associated with editing apparatus occurs when one or more source tapes have several scenes recorded thereon. Typically, the editor merges segments of video program information from a particular scene, thereby carrying out a scene-by-scene editing operation. When the editor wishes to make corrections or revisions to an edited tape, for example, if an additional segment is to be merged, or if the sequence of merged segments is to be changed, or if a particular segment is to be replaced with a special effects processed signal, such corrections or revisions may affect other scenes on the edit tape which are not changed because they, nevertheless, require the laborious task of correction to be compatible with the re-edited scene.